The Herald can reveal that the Irish rugby star and his wife Laura are expecting their first child.
The 28-year-old former Leinster player and his other half are preparing to welcome a son or daughter within weeks of their first wedding anniversary this summer.
Laura (27) is five months into her pregnancy and the couple, who are based in Paris while Jonathan is signed to play for French club Racing Metro 92, told members of their family as well as close friends the happy news last month.
It will be the first grandchild for Jonathan's parents Gerry and Claire and a source close to the family told the Herald that they are "absolutely delighted".
Laura, who worked as a secondary school teacher at Loreto on the Green in Dublin until moving to Paris last year, flew to London to support Jonathan as Ireland took on England in their first away match of the 2014 Six Nations campaign at the weekend.
Jonathan's father Gerry was also supporting the out half in the stands at Twickenham.
The childhood sweethearts have been together for nearly 15 years.
Jonathan and Laura first met in Rathgar Tennis Club in Dublin when they were just 13 and the couple tied the knot last July in in Adare, Co Limerick, days after Jonathan returned from duty on the successful Lions tour of Australia.
They made their vows in the 13th century Holy Trinity Church, with dozens of fans waiting outside to cheer them on, before going to the nearby Adare Manor for a lavish wedding reception.
A string of Jonathan's Ireland and Leinster team mates also attended, including Rob Kearney, Brian O'Driscoll, Leo Cullen and Cian Healy.
After becoming husband and wife, Jonathan and Laura set up home in the French capital ahead of his debut season as the highest-paid player in European rugby.
They now live in the Parisian suburb Chatenay-Malabry, just 10km from the bustling city centre.
It was a disappointing day for Ireland at Twickenham on Saturday, but despite the narrow three-point defeat there is still a silver lining for Joe Schmidt's side.
With the boys in green top of the leader board in points difference, the Six Nations championship is still a possibility for the Irish team.