Billy Joel's ex-wife is ''really happy'' that he is to be a father again.

The 'Piano Man' hitmaker and girlfriend Alexis Roderick are expecting their first child together and Katie Lee - who was married to the 65-year-old star for six years until 2010 - thinks he is a ''terrific'' dad.

Speaking about Billy - who already has 29-year-old daughter Alexa with ex-wife Christie Brinkley - and Alexis, Katie told 'Extra': ''I'm really happy for them. He's a great guy, he deserves all the happiness in the world, and he's a terrific father, so I'm really, really happy.

''He will always be in my life, and I think he's just the greatest.''

A spokesperson for the 'Uptown Girl' singer confirmed the news earlier this week but the couple plan to keep further details about their unborn baby under wraps until after the birth.

The singer started dating former banker Alexis in 2009 and rumours began swirling that they got engaged earlier this year.

A source said in February: ''They're looking at a summer wedding. He's happier than ever.''

The musician presented Alexis with a diamond ring more than two years ago, but is said to have only asked her to marry him recently.

The insider added: ''That ring wasn't an engagement ring - more like a friendship ring. But he came to realise that he wasn't being fair to Alexis. He knew he couldn't keep stringing her along forever.''

Aside from Christie and Katie, Billy was also previously married to Elizabeth Weber from 1973 to 1982.