Is your Valentine's Day diamond a FAKE? Expert reveals a simple trick to prove your engagement ring is the real deal with a sheet of white paper and a pen

• The founder of Europe's biggest online diamond jeweller spoke to Femail 
• He revealed the 5 questions to ask to spot a fake diamond including temperature
• Other tests includes a 'line test' and the amount jewel sparkles to see if its real

It's one of the most popular days of the year to propose and all across the country, many are hoping that a little box containing a sparkling diamond is awaiting them on Valentine's Day. 

But whether you're in the market for purchasing an engagement ring, or the lucky recipient, how can you tell if  an expensive sparkler is the real deal? 

FEMAIL spoke to expert Tobias Kormind, who is founder of 77 Diamonds, Europe’s largest online diamond jeweller.

Tucked away behind Oxford Street in London's Mayfair Tobias' workshop and showroom supplies jewellery to order for the likes of Premiership footballers, supermodels, millionaires and even billionaires.

Here he shares the five questions you should ask to check if a diamond is authentic. 

1. IS IT COLD? 

Tobias explained: 'Diamonds are excellent thermal conductors, so will be cold to the touch. 

'A fake diamond will be at room temperature.

2. WHAT DOES IT LOOK LIKE IN THE SUN?

'About 50 per cent of real diamonds will fluoresce or glow blue under long wave UV light. 

'If the diamond doesn't glow, it is an indicator it may be fake' he added. 

3. HOW MUCH DOES IT SPARKLE? 

'A real diamond will sparkle more than a fake. 

'This is not a very accurate test, but will catch poor quality fakes' Tobais continues.

4. DOES IT PAST THE LINE TEST? 

Tobias also explained how a line test can help with tell a fake apart from a real diamond.

'For round stones, draw a black line on a white piece of paper and turn the diamond upside down. 

'Move the diamond back and forth over the line. 

'If you can see the line through the diamond, it is fake.

IS IT IMPERFECT?  

Surprisingly, Tobias added that the more imperfections the jewel has, the more likely it is that it's real

'Many lower quality diamonds will have small visible inclusions which are particles inside that look like dirt' he explained.

'If you can spot something like this inside, it may be a good indicator that the diamond is real.'

And if you're still unsure... 

If you're unsure after the five steps, Tobias explained that you can use professional tools to determine if a diamond is legitimate.

'You can buy a diamond tester for about £300-400 which will tell you if the stone is a real diamond or a simulant like cubic zirconia or moissanite' he said.

'The most definitive way to determine if a diamond is real is to send it off to a credible laboratory like the GIA (Gemological Institute of America), which will not only determine whether it is a real or fake diamond, but can determine if it is man-made, has been treated with heat or pressure, or is 100 per cent natural.