Justin Bieber picked out a specific diamond for Hailey Baldwin's engagement ring after seeing her face in the gem.

The 'Never Say Never' hitmaker had a big hand in helping to design the $500,000 band for his 21-year-old fiancée, who he popped the question to last week, and his jeweller Jack Solow admitted the 24-year-old star was ''really excited'' about the process.

He said: ''I showed him all the details and all the intricacies like I would give any other 25-year-old boy who would come to the office to buy an engagement ring.

''He seemed really excited. He was looking inside the diamond with the loupe, and said 'I think I see Hailey's face.'

''In the end, Justin wanted something that would gracefully accentuate Hailey's beautifully-shaped hands.

''We settled on an oval stone that was just exceptional in its length and grace. Look at her hands - she's exquisite.''

Following Justin's purchase, Jack made a $5,000 donation to Hailey's grandmother's breast cancer charity through his family-run New York store Solow & Co ''out of respect'' for the couple.

He said: ''We made $5,000 donation to her grandmother's breast cancer charity, the Carol M. Baldwin Breast Cancer Fund, out of respect for the couple and to mark the moment.''

The charity has confirmed the pledge, writing on Instagram: ''We want to congratulate Carol Baldwin's granddaughter @haileybaldwin on her engagement. Thank you @solowco for your generous donation. (sic)''

Jack revealed Justin's manager Scooter Braun encouraged him to use the private jeweller to find the perfect engagement ring for Hailey.

He added to PEOPLE: ''Justin did have a hand in selecting the diamond because I sent videos to his team. I know him through [his manager] Scooter Braun.

''When it came time to find a ring, Justin asked Scooter and said, 'I'm ready to pop the question' and he said, 'There is only one place to go, ask Jack.''